The Warner Gear Division of Borg-Warner Corporation located at Muncie, Indiana, manufactures a single-speed transmission known as a Model PR1 Power Ranger Shuttle Transmission. This transmission is used with a Model No. W11 torque converter manufactured by the Borg & Beck Division of Borg-Warner Corporation and located at Sterling Heights, Michigan. That transmission and associated hydraulic torque converter find particular utility in the power train of a fork lift truck, for example.
The referenced transmission and torque converter has heretofore utilized a transmission control system that has experienced fluid flow control problems including undesirable pressure fluctuations at the fluid inlet passage to the torque converter. Moreover, a pressure relief valve or regulator incorporated in that transmission control system has undesirably relieved an excessive proportion of fluid from the inlet passage of the torque converter directly to the outlet of a cooler which receives and cools fluid from the outlet passage of the torque converter. Thus, under certain conditions an undesirable portion of the circulating fluid bypasses the cooler via that relief valve, so that the torque converter cooler flow rate did not uniformly increase over the operating range as desired.
A large number of valves are known which can modulate and control the fluid flow rate to and from a torque converter or alternately the pressure at the inlet and/or outlet thereof. Some valves can even control multiple combinations of these parameters. However, these valves are not only usually complex and costly in construction, but also they take up valuable room where space is at a premium. Still further, what is needed is a solution to the aforementioned problems that can be incorporated in commercially available transmission control systems with but minimal delay to the ultimate consumer.
The present invention is directed to overcoming one or more of the problems as set forth above.